Dye sensitization of electrophotographic material

ABSTRACT

AN INDOANILINE DYE IS EMPLOYED IN CONJUNCTION WITH A CONVENTIONAL SENSITIZING DYE EFFECTIVE WITHIN THE REGION OF 530 TO 550 NM. FOR SPECTRALLY SENSITIZING A PHOTOCONDUCTIVE RECORDING MATERIAL CONTAINING PHOTOCONDUCTIVE ZINC OXIDE POWDER DISPERSED IN A BINDER. THE INDOANILINE DYES HAVE STRONG SENSITIZING EFFECTS IN THE REGION ABOVE 600 NM. AND ARE SUBSTANTIALLY STABLE TO LIGHT, AND IN CONJUNCTION WITH THE CONVENTIONAL SENSITIZING DYE IMPARTS A LONG-LASTING OFF-WHITE APPEARANCE TO THE RECORDING MATERIAL.

Jan. 19, 1971 E. VERHILLE 3,556,786

DYE SENsIT IZATION OF ELECTROPHOTOGRAPHIQ MATERIAL Filed May 19, 1967 2 Sheets5heet 1 FIG.

. INVENTUR Wand; 50.1511) 644 d411,,

ATT( )HNFYS Jan. 19, 1971 K. E. VERHILLE 3,556,786

DYE SENSITIZATION OF ELECTROPHQQOGRAPHIC MATERIAL Filed May 19. 1967 2 Sheets-Sheet 2 FIG. 2

INVENT( )R KKQJLIC 5. 6m, ilt i [IL] 3,556,786 DYE SENSITIZATION F ELECTRO- PHOTOGRAPHIC MATERIAL Karel Eugeen Verhille, Mortsel, Belgium, assignor to Gevaert-Agfa N.V., Mortsel, Belgium, a Belgian com- Filed May 19, 1967, Ser. No. 639,905 Claims priority, application Great Britain, May 20, 1966, 22,631/ 66 Int. Cl. 603g 5/08, 7/00 US. Cl. 961.7 6 Claims ABSTRACT OF THE DISCLOSURE United States Patent 0 600 nm. and are substantially stable to light, and in conjunction with the conventional sensitizing dye imparts a long-lasting off-white appearance to the recording material.

This invention relates to photoconductive materials, and more particularly to photoconductive materials or compositions containing a dye that mainly absorbs in the read and near-infrared region of the spectrum.

It is known in electrophotography to use photoconductive materials for the recording of electromagnetic radiation patterns in terms of diiferences in charge density or electroconductivity.

Electrophotographic materials consisting of a support, on which a photoconductive substance is coated together with a binder are generally known in this respect. As photoconductive substances in such coatings specific inorganic as well as organic substances can be used, e.g. sulphur, selenium and compounds belonging to the type of the oxides, sulphides and selenides of zinc, cadmium, mercury, antimony, bismuth,titanium and lead, anthracene, anthraquinone, and a many recently discovered organic monomeric and polymeric photoconductors.

Among these photoconductors photoconductive zinc oxide has been selected for its high inherent sensitivity and brilliant white colour. Zinc oxide constitutes an excellent contrasting base for developer materials applied thereto.

Since photoconductive zinc oxide has little or no absorption power for light of the visible spectrum, it has sitivity and increase the total sensitivity of this zinc "oxide with dyes absorbing light in one or more ranges of the visible spectrum. I

However, the incorporation of such sensitising subbecome standard practice to extend the spectral sen:

stances has the inherent disadvantage of imparting to the recording layer a coloration, which may be strongly objectionable in the manufacture of colour prints and/or may be unwanted from an aesthetic viewpoint. Therefore,

several attempts have been made'to remedy this inconv length, would bleach the dye(s), thereby imparting a P neutral background to the recording material. Such sensitisers, which bleach out easily loose relatively quickly their sensitising action during storage of the electrophotographic material and also cannot be handled in daylight for extended periods of time.

A 3,556,786 Patented Jan. 19, 1971 In order to circumvent the use of bleachable dyes and to still obtain recording layers with a low colouration, a combination of dyes with high fastness to light can be used, which with regard to each other have a complementary colour. When using such dyes in proper proportions, a zinc oxide with a barely perceptable colouration can be obtained (see eg Example 2 of the United States patent specification 2,987,395 of James G. Jarvis, issued June 6,1961).

Whereas the human eye is most sensitive to light within a small wavelength range around 550 nm., the colouration of a zinc oxide layer sensitised with a dye absorbing around this wavelength, appears much higher to the standard observer than a zinc oxide layer sensitised in the other regions of the visible spectrum. Therefore, it has become common practice to sensitise a zinc oxide material with at least two dyes respectively absorbing in theregion near 480 nm. and 580 nm. in order to obtain an off-white zinc oxide material.

In some instances, however, the use of dyes absorbing near the wavelength of maximum sensitivity for the human eye, i.e. around 530 to 550 nm., may be necessary. This is for instance the case for colour prints on zinc oxide paper, wherein the sensitivity has to extend over the entire visible spectrum. Another reason for sensitising the zinc oxide material with sensitising dyes mainly obsorbing near 530 to 550 nm. resides in the possibility of making use of such interesting cold printing light sources as fluorescent tubes. Among these, the ones containing a green light-emitting phosphor (maximum of emission near 527 nm.) are the most interesting since they yield the highest amount of photons per watt. The technological features concurrent with such type of fluorescent tubes are so attractive that the application of this type of light souil'jcles in electrophotographic printing is particularly desira e.

When sensitising a photoconductive material without colour haze in said region of the visible spectrum of 530 to 550 nm. it is preferred to use at least one complementary dye absorbing beyond 600 nm., more preferably in the region around 700 nm. Dyes absorbing in that region are already known, e.g. pentamethine and hepta methine dyes such as those described in the Unitedf States patent specification 3,002,835 of Joze Kostelec, issued Oct. 10, 1961. These dyes, being in general not veryflstable to light, are less suited for a permanent sensitisat ion of the photoconductive substance or masking of the colouration of the sensitising dye, mainly absorbing in the region of 530 to 550 nm.

It has been found now that quinone-imine dyes, absorbing in the region of the visible spectrum above 600 nm., are very suited to accomplish the requirements set forth above and moreover are substantially stable to light. Among these quinone-imine dyes indoaniline dyes are particularly useful, more particularly those represented by the following general formula:

wherein R represents hydrogen or a substituent, more particularly of the type known in quinone-imine dye chemistry e.g. a substituent present in the structure of a colour coupler for cyan used in silver halide colour photography, e.g. a N alkyl substituted carbamyl group, a N-aryl-substit uted carbamyl group or a sulpho- R represents a p-dialkyl-aininophenyl group including a substituted p-dialkylaminophenyl group, e.g. N tR2 represents-the residue of acoupled aromatic primary amino colour developer used in silver halide colour "photography, and e Z represents the necessary atoms to close an aromatic: ring" system, including a substitutedring syste-m,e.g'. t the benzene series and naphthalene series, but-preferably of'the naphthalene series v For representatives of colour couplers suited for the production ofquinone-imine dyes referenceis made,;e.g., to lafkides Photographic Chemistry-Vol. II (1960) Fountain Press.London, pp. 53 6-537 and the United Kingdom patent specifications 831,731 filed June 20, 1957, 939,030 filed Oct. 31, 1960, 975,939 filed Nov. 18, 19.60,, 975,928 filed Ian. 31, 1961, 983,648. filed May 8, 1961, 975,773 filed Sept. 4, 1961, 955,009 filed Oct. 2, 1961, 969,921 filed Oct. 20, 1961 and the cognate 1,004,- 2.81 filingdates Feb. 15, 1961 and Feb. 12, 1962, all of them by Gevaert Photo-Producten N.V.

Particularly suitable representatives falling under the scope of the above-cited general formula are listed in Table I, which table also indicates the absorption maxima of the dyes and the relative speed obtained from tests as described in Example 1. The relative speed is expressed in respect of a non-coloured zinc oxide material, to which has been given arbitrarily the speed value 100.

TABLE I Absorption maximum Relative Structural formula speed l WFS Oz-Q-Glig 680 225 Y In: 1. AB 1I Y ontinued I 1' Absorption maxi- Relative Structural fonnula I mum speed 0 N 02 ll I W43 ONH' 720' 220 I N l 9 I] l l CO-NHQ 720 225 0 l5 TOONHON 720 230 l N l TABLE I. Cntinued Absorption maxi- Relative Structural formula mum speed 0 11 we O-NH-Q-C 0 OH 720 215 CzHs II I

H o O-NHQ 710 230 Y N I I C 2H5 O ll Wl(3 ONHSO2CH3 710 225 EXAMPLE 1 To 1,500 g. of ethylene chloride were added consecutively:

36 g. of ethylcellulose having a degree of substitution of 2.45 of ethyl groups (a 5% solution in toluene/ethanol (80/20) has a viscosity of 68 cps. at 25 C.), and

900 g. of zinc oxide (Type Blanc de Neige, Vieille Montagne, Hollogne-aux-Pierres, Belgium).

This mixture was ground in a sand-mill whereupon 391 g. of a 20% solution of copoly( viny1 acetate/vinyl laurate) (80/20) in ethylene chloride were added together with a mixture of 65 g. of ethanol, 212 g. of ethylene dichloride and 31 g. of a 10% solution of monobutyl phosphate in ethanol. To the obtained mixture 90 ccs. of a 0.1% solution of one of the dyes, listed in Table I, in ethanol were added.

The resulting compositions were coated on a glassine paper support weighing 65 g./sq. m., pro rata of 19 g. of zinc oxide per sq. m.

The materials were then negatively charged with a corona, the potential difference between the wires and the ground being -6,000 v. The charged materials were exposed through a step wedge with a constant 0.1 by means of an incandescent lamp of 450 watt with a radiation intensity of 2,280 lux.

Subsequently, the differently sensitised materials were electrophoretically developed in the same conditions. The relative speed values are stated in Table I.

Apart from their use as spectral sensitising agent in the near infrared as illustrated in Example 1, the quinoneimine dyes are preferably used as complementary dyes in combination with spectral sensitisers for the range 480 to 5 nm.

Examples of such combinations of dyes are described in Examples 2 and 3.

Since any suitable resin may be employed as binding agent for the photoconductive zinc oxide, reference is particularly made to those described in the Belgian patent specification 612,102 filed Dec. 29, 1961 by Gevaert Photo-Producten N.V. The said binding agents are soluble in an organic solvent and are usually applied as an organic solution containing the photoconductive zinc oxide dispersed therein. A particularly suitable binding agent composition for application from an organic solvent or mixture of solvents is a mixture of ethylcellulose and a copoly(vinyl acetate/vinyl laurate) (80/20). In this mixture preferably up to 30% by weight of ethylcellulose is provided.

Suitable resin compositions, which can be applied from a solution in water, are those described in our published Dutch patent applications 6608815, 6608814 and 6608816, all of them filed June 24, 1966.

The ratio of photoconductor with respect to binder is preferably comprised between 50 and by volume. In order to increase the dark resistivity of the photoconductive zinc oxide, use can be made of acid substances and salts thereof described in the Belgian patent specification 6l2,102 filed Dec. 29, 1961 by Gevaert Photo- Producten N.V. Among these additives partially esteri-fied oxyacids derived from phosphorus, e.g. acid butyl phosphate, are preferred.

The photoconductive coating composition containing the quinino-imine dyestuif can be coated on a support by a known coating technique, e.g. by spraying, whirling, dip-coating, or by a coating technique wherein use is made of a doctor blade. The supports or base materials are chosen in view of the particular charging, exposing, recording, developing and/ or transfer technique wherein the recording material has to be used.

In electrophotographic recording techniques wherein the photoconductive material is non-differentially electrostatically charged and image-wise discharged by imagewise exposure to light, the support preferably possesses an electric volume resistivity that is considerably lower than that of the recording layer. Suitable supports are described, e.g. in the United Kingdom patent specifications 995,491 filed Mar. 16, 1962, 1,020,503 filed Nov. 8, 1961 and 1,020,504 filed Dec. 29, 1961 all by Gevaert Photo-Producten N.V.

EXAMPLE 2 To 1000 ccs. of ethylene chloride were added consecutively:

300 g. of zinc oxide (type Blanc de Neige, Vieille Montagne, Hollogne-aux-Pierres, Belgium),

18 g. of copoly(vinyl acetate/vinyl laurate) (80/20),

12 g. of ethylcellulose having a degree of substitution of 2.45 of ethyl groups (a 5% solution in toluene/ethanol (80/20) has a viscosity of 6-8 cps. at 25 C.),

12 ccs. of a 10% solution of monobutyl phosphate in ethanol,

144 ccs. of a 0.25% solution of Erichrome Geranol-R (Cl. 43,865) in ethanol,

7 0.021 g. of the compound corresponding to the structural formula:

C2115 l N CzHs The composition was intimately mixed in a sand-mill and then coated on a glassine paper support weighing 65 g./sq. m., pro rata of 19 g. of zinc oxide per sq. m.

The resulting material was negatively charged with a corona, the potential difference between the wires and the ground being 6,000 v. The charged material was exposed through a step wedge with a constant 0.1 by means of an incandescent lamp of 450 watt with a radiation intensity of 2,280 lux. Subsequently, the material was developed electrophoretically.

The sensitivity of the obtained recording layer was expressed by the number of steps corresponding with the discharged areas wherein no developing powder was deposited, thus having the original density of the recording layer. The higher that number, the more sensitive is the layer. The number of non-blackened steps obtained in this example was 20.

The reflexion curve (percent reflexion versus wavelength in nanometer) of the material obtained is shown in FIG. 1. I

The reflexion values at the various wavelengths were obtained with a spectrophotometer versus magnesium oxide as standard.

EXAMPLE 3 To 1,000 cos. of ethylene chloride were added consecutively:

300 g. of zinc oxide,

51 g. of copoly(vinyl acetate/vinyl laurate) (80/20),

51 g. of ethylcellulose having a degree of substitution of 2.45 of ethyl groups (a 5% solution in toluene/ethanol (80/20) has a viscosity of 6-8 cps. at 25 C.),

13 cos. of a 10% solution of monobutyl phosphate in ethanol,

13 ccs. of a 10% solution of tetrachlorophthalic anhydride in ethanol,

15 ccs. of a 1% solution of Eriochrome Cyanine R (C.I.

43,820) in ethanol,

0.027 g. of a compound corresponding to the structural formula:

12 ccs. of a 0.25% solution of Orange Acridine Brillante EZ (Cl. 46,005 in ethanol.

The composition was mixed and coated as described in Example 2.

The resulting material was then further treated as described in Example 2. The number of non-blackened steps obtained in this example was 24.

The reflection curve of the material obtained is shown in FIG. 2 (percent reflection versus wavelength in nanometer).

I claim:

1. A photoconductive recording material containing a photoconductive recording layer comprising photoconductive zinc oxide in finely divided particle form dispersed in a binder, a spectrally sensitizing dye for said zinc oxide sensitizing in the region of about 530 to 550 nm., and a quinone-imine dye, which is represented by the following general formula:

wherein:

R is hydrogen, or a substituent of the type known in quinone-imine dye chemistry and selected from the group consisting of a N-alkyl-substituted carbamyl group, a N-aryl-substituted carbamyl group or a sulphoaryl group,

R is a p-dialkyl-aminophenyl group, and

Z represents the necessary atoms to close an aromatic ring system, said quinone-imine dye increasing the spectral sensitivity of the recording layer in the region of about 600-700 nm.

2. A photoconductive recording material according to claim 1 wherein said quinone-imine dye sensitizes the photoconductive layer in the region of 600 to 700 nm.

3. A photoconductive recording material according to claim 1, wherein the binder substantially consists of a mixture of ethyl-cellulose and a copoly(vinyl acetate/ vinyl laurate).

4. A photoconductive recording material according to claim 3, wherein that mixture contains up to 50% by weight of ethylcellulose.

5. A photoconductive recording material according to claim 1, where in the spectrally sensitising dye, sensitising in the region of 530 to 550 nm., is Eriochrom Geranol-R (Cl. 43,865).

6. A photoconductive recording material according to claim 1, wherein the spectrally sensitising dye, sensitising in the region of 530 to 550 nm. is Eriochrom-Cyanine-R (C.I. 43,820).

References Cited UNITED STATES PATENTS .8/ 1961 Sugarman et a1. 961.7 9/ 1962 Greig 961.7

' US. Cl. X.R. 252-501 

